Coating composition for electrodeposition coating

ABSTRACT

AQUEOUS SOLUTION FOR COATING METAL SURFACES BY ELECTRODEPOSITION WHEREIN MAIN ELEMENT IS A COPOLYMER OF AN ACRYLATE, ANOTHER ETHYLENICALLY UNSATURATED MONOMER, A DICARBOXYLIC ACID AND AN ALKOXYALKYLACRYLAMIDE. THE BEHAVIOR OF THE ACID RESIN IN WATER IS DEFINED BY PH=PKA +N LOG (X/1-X). EXCELLENT ONE-COAT SURFACE GLOSS IS ACHIEVED WHEN PAK, THE ACIDITY OF THE RESIN, IS AT LEAST 8.0, N, A PARAMETER BASED ON THE EXTENSION OF THE RESIN IN WATER, IS IN THE RANGE 0.5-1.5, AND X, THE NEUTRALIZATION DEGREE, IS 30-8/%. THE RESIN IS SELF-CROSS LINKING, BUT DURABILITY OF THE FILM IS ENHANCED WHEN AN EPOXY OR MELAMINE RESIN IS ADDED. A PIGMENT HAVING AN ACIDITY PKP WEREIN THE ABSOLUTE VALUE OF THE DIFFERENCE PKP-PKA IS AT LEAST 0.1 MAY BE INCORPORATED IN THE AQUEOUS SOLUTION.

United States Patent 3,652,478 COATING COMPOSITION FOR ELECTRO-DEPOSITION COATING Masao Ishii, Tokyo, and Takashi Sunamori and SadaoKimura, Ohtake-shi, Japan, assignors to Mitsubishi Rayon Co., Ltd.,Tokyo, Japan No Drawing. Filed Oct. 15, 1968, Ser. No. 767,818 Claimspriority, application Japan, Oct. 27, 1967,

42/69,146, 42/69,147 Int. Cl. C08f /40 US. Cl. 260-294 UA 13 ClaimsABSTRACT OF THE DISCLOSURE Aqueous solution for coating metal surfacesby electrodeposition wherein main element is a copolymer of an acrylate,another ethylenically unsaturated monomer, a dicarboxylic acid and anal-koxyalkylacrylamide. The behavior of the acid resin in water isdefined by pH=pKa +n log (oz/l-ot). Excellent one-coat surface gloss isachieved when paK, the acidity of the resin, is at least 8.0, n, aparameter based on the extension of the resin in Water, is in the range0.5-1.5, and a, the neutralization degree, is 30-80%. The resin isself-cross linking, but durability of the film is enhanced when an epoxyor melamine resin is added. A pigment having an acidity pKp werein theabsolute value of the difference pKp-pKa is at least 0.1 may beincorporated in the aqueous solution.

This invention relates to a coating composition suitable for use inelectrodeposition coating methods. More particularly, the inventionpertains to a coating composition for electrodeposition coating which,according to an electrodeposition coating method and by one-coat finish,can form on the surface of a metal a film having excellent surface glossand various prominent characteristics of a thermosetting resin.

For the purpose of imparting corrosion resistance and beautifulappearance to metal materials, water-type or organic solvent-typecoating materials have heretofore been applied to the metal materials byspray-coating, rollcoating, curtain flow coating, dip-coating or thelike method. Recently, however, attention has come to be paid toelectrodeposition coating methods using water-type coating materialswhich have such advantages that the resulting films are uniform; evensuch metal materials as being complex in shape can be easily coated; nodanger of fire is encountered in the coating steps; no sanitary problemis brought about; and the reduction in cost is possible due to centralcontrolling of the coating steps. As processes for perparing coatingcompositions usable in such electrodeposition coating methods, therehave been known the processes disclosed in U.S. Pat. No. 3,230,162 andBritish Pat. Nos. 1,030,425, 1,027,813 and 1,115,130. However, coatingcompositions obtained according to said processes are marked incloration of the resulting films and, even in the case of those which donot bring about the coloration of the resulting film's, they cannot formfilms, which have, in combination, an anti-rust property necessary forprotective films for metals and a beautiful appearance showing excellentsurface gloss. Accordingly, they are chiefly employed as mere coatingmaterials for under coating. Thus, there has not yet been obtained anycoating material for electrodeposition coating which can sufficientlydisplay the advantages of electrodeposition coating method and can givea film excellent in efficiencies by only one-time application withoutrequiring any over coat finishing.

Conventional electrodeposition coating materials mostly contain, as thebinder resin, highly water-soluble resins composed a large amount ofdissociating functional groups for effecting electrophoresis and a largeamount of hydrophilic functional group, and hence are favorable inadhesion to materials to be coated. However, they have such drawbacksthat bubbles are liable to be trapped in the resulting films; they arehigh in water-solubility so that the resulting films are low in heatfiowability at elevated temperatures to make it impossible to obtainexcellent surface gloss; and they contain highly water-soluble resinsand therefore the films obtained after baking are great in sensitivityto water and low in anti-rust property. Accordingly, it has beenimpossible to use them as coating compositions for electrodepositioncoating which are usable for one-coat finish.

With an aim to improve the water resistance of the resulting films,British Pat. No. 1,027,813 provides a coating material prepared byforming an acrylamide copolymer and then treating the polymer withparaformaldehyde to convert the amide group into an N-methylolamidegroup, and British Pat. No. 1,115,130 provides a coating materialprepared by butoxymethylating a part of N- methylolamide group of anacrylic coating material containing an N-methylolarnide group. Thesecoating materials, however, are still high in water solubility and therefore it is impossible to obtain therefrom, according toelectrodeposition coating method and by one-coat finish, films having,in combination, excellent surface gloss and prominent physical andchemical properties.

In the practice of electrodeposition coating, a great present inventorsmade various studies to find that in order to obtain, according toelectrodeposition method and by one-coat finish, a film having, incombination, excellent surface gloss and various prominentcharacteristics owned by thermosetting coating materials, it isnecessary that the amount of hydrophilic functional group in the binderresin component of the coating material be made as small as possible sofar as the resin component can be stably dispersed in water to enhancethe flow characteristics of the coating material at the elevatedtemperature, thereby improving the resulting film in surface gloss aswell as in anti-rust property.

In the practice of electrodeposition coating, a great factor to make theresulting film always uniform is that the electrodeposition coating bathshould not cause any variation due to lapse of time. However, in thecase of a conventional coating material using a highly watersolubleresin component as a hinder, the dissolved state of the resin componentin water varies with lapse of time, and therefore the stability of theelectrodeposition coating bath is deterioriated. Further, apolymerization solvent employed in preparing a resin solution differs,in general, from a solvent necessary for dispersing a resin in water,and therefore, in dispersing the resin in water, it is necessary toeffect solvent substitution. If the polymerization solvent is leftdepending on the procedure of said solvent substitution, or when thedissolved state of the resin undergoes variation due to said solventsubstitution treatment, the stability of the electrodeposition coatingbath is lowered in some cases. Further, in the case of a coatingmaterial containing a pigment, the stability of the emulsion is greatlyafiected not only by the properties of the resin employed but also bythose of the pigment employed.

Based on such a detailed knowledge as mentioned above, the presentinventors made studies to accomplish the present invention relating to acoating composition for electrodeposition coating which can give byone-coat finish a film having excellent surface gloss and prominentphysical and chemical characteristics, in which is used as a maincomponent a copolymer obtained from an N-alkoxyalkyl (meth)acrylamidemonomer, itaconic or amethyleneglutaric acid and other copolymerizablevinyl monomer.

It is therefore a primary object of the present invention to provide acoating composition for electrodeposition coating which is favorable instability of electrodeposition coating bath and which can form,according to electrodeposition coating method and by one-coat finish, afilm having excellent surface gloss and physical and chemicalcharacteristics, which coating composition comprises a coating materialcontaining as a main component a watersoluble or water-dispersibleresin, which is a copolymer obtained from anN-alkoxyalkyl(meth)acrylamide monomer, itaconic or a-methyleneglutaricacid, and other copolymerizable vinyl monomer, said copolymer having anacidity represented by pKa of at least 8.0, a polymer chain extensionrepresented by parameter n of from 0.5 to 1.5, a neutralization degreerepresented by a of from 30-80% (per mole of carboxyl group; the sameshall apply hereinafter), a glass transition temperature of 60 C. orbelow, and a number average molecular weight of 20,000 or less.

A secondary object of the invention is to provide said coatingcomposition for electrodeposition coating which is favorable in bathstability, characterized in that it contains a pigment capable ofsatisfying the [pKp-pKa} 20.1, wherein pKp represents the acidity of thepigment; and pKa represents the acidity of the resin.

The characteristic of resin which are for the achievement of the primarobject of the present invention will be examined below.

As to the behaviors of acids in high polymer in water, it has beenknown, in general, that in the region where on is not excessively low orhigh, there is established the following equation:

wherein pKa represents the acidity of the resin; 12 is a parametershowing the extension of polymer chain; represents the neutralizationdegree of the resin; and pH represents the pH of the aqueous solution oremulsion of the resin deposition coating bath.

The values of pKa and n are indexes representing the hydrophilicproperty of the resin, and vary depending on the composition of theresin. For example, in the case of a polymer containing a large amountof an acid, which is a dissociating functional group, or of anon-dissociating hydrophilic functional group, the value of pKadecreases and the value of It increases in proportion to the contents ofsaid functional groups. On the other hand, when the content of acid ismaintained constant and the content of hydrophilic functional group islowered, the value of pKa increases and the value of n is maintainedsubstantially constant. Whether a resin is water-soluble orwater-dispersible is decided according to the values of pKa, n and a,and a resin, which is great in pKa value or which is low in 21. valueand becomes more water-dispersible.

In order to obtain a film having excellent surface gloss and prominentphysical and chemical characteristics, according to electrodepositioncoating method and by onecoat finish, the present inventors studied,based on the above-mentioned knowledge, the usable ranges of pKa, n anda, to find the facts described below.

That is, when a resin component low in pKa value is used, the resultingelectrodeposition coating bath becomes acidic even if the neutralizationdegree of resin is made high and, depending on the kind of metal, thereare some cases where the generation of rust is observed on the metalsurface during the electrodeposition coating process. Further, a resincomponent low in pKa value is high in solubility for water, and highpolymer constituting the resin are entangled each other and areelectrodeposited in the entangled state on the surface of metal to becoated. Accordingly, the resulting film is low in heat refiowability andhas no smooth surface gloss. On the other hand, a resin component havinga great pKa value is not dissolved in Water even though theneutralization degree of the resin is made high, but is brought into adispersed state. Since the dispersed particles tend to adhere to oneanother, the film-forming ability of the resin component during theelectrodeposition coating process is lowered and the dispersionstability of the resin in the electrodeposition coating bath is injured.With increasing pKa value, however, the heat refiowability of the resinis improved and the surface gloss of the resulting film is increased. Inthe present invention, the value of pKa was measured when the bathconcentration was 11% by weight and the temperature was 25 C.

An examination of the 12 value shows the following:

In Water, the 11 value of a Water-soluble high polymer tends to vary, ingeneral, from a certain value to 1. Although no ground for saidphenomenon has been clarified yet, it is interpreted that the phenomenonis ascribable to the orientation, into the water phase, of thehydrophilic functional groups constituting the resin component, and tothe process of dispersion into water of high polymer due to a chemicalforce. In fact, an aqueous bath containing high polymer of 11:1 does notcause any variation due to lapse of time. Further, with the variation ofn value due to lapse of time, the value of pKa tends to decrease due tolapse of time, as well, whereby the electrodeposition coating bath islowered in pH and in specific resistance. In case such a resin is usedas a coating material for electrodeposition coating, theelectrodeposition coating bath formed by use thereof undesirably becomesunstable with lapse of time.

In an electrodeposition coating method in which onecoat finish iseffected, it is, of course, necessary that the film obtained afterbaking should have practical properties. In order to obtain a filmhaving excellent surface gloss, however, it is necessary that the filmformed at the time of electrodeposition coating should have heatrefiowability. As to the ability of forming an electrodeposited film,the glass transition temperature, represented by Tg, of the highmolecular weight substance constituting the resin component becomes animportant factor. In case a resin component high in Tg is used, theadhesion of dispersed particles of coating material difficulty takesplace, so that the film formed on the surface of a metal to be coated isnot increased in electric resistance and is undesirably lowered inthrowing power. Further, the heat refiowability of film at the time ofcuring becomes inferior, and the gloss of the film obtained cannot besaid to be favorable.

The molecular weight of resin also is an important factor. In case aresin high in molecular weight is used, there is observed the samephenomenon as in the case where a resin high in Tg is used. Further, notonly the value of pKa is lowered but also the value of n is liable toincrease. Accordingly, the use of a resin high in molecular weight isnot desirable.

The glass transition temperature Tg referred to herein signifies the Tgof a copolymer comprising monomer units other than cross linkingfunctional monomer, and is calculated according to the equation 1/Tg=WTg +W /Tg [II] wherein W, and W represent, by weight percent, theproportions of individual monomers constituting the polymer component,assuming that the proportion of the polymer comprising other monomersthan cross linking functional monomer is and Tg and Tg represent theglass transition temperatures of homopolymers of individual monomerconstituting the polymer.

Further, the molecular weight is a number average molecular weightcalculated according to osmotic pressure method. The range of molecularweights suitable for one coat finish is from 5,000 to 20,000 If themolecular weight is less than 5,000, the polymer is undesirably loweredin water dispersibility, and if the molecular weight is more than20,000, the polymer tends to be lowered in pKa value, and theelectrodeposition characteristics thereof are undesirably lowered.

Accordingly, the required conditions for obtaining a film havingexcellent surface gloss and prominent film properties, according toelectrodeposition coating method and by one-coat finish, are such thatthe high polymer constituting the coating composition employed shouldhave such characteristics as an acidity pKa of at least 8.0, a parametern of from 0.5 to 1.5, a neutralization degree a of from 30 to 80%, aglass transition temperature 'Tg of 60 C. or below, and an averagemolecular weight of 20,000 or less. Particularly when the bath stabilityis to be sutficiently secured, it is necessary that theelectrodeposition coating bath should contain as a main component -220%by weight of a resin having pKa of from 8.5 to 9.5; n of from 0.8 to1.3; Tg of 30 C. or below, preferably from -25' to 10 C.; and an averagemolecular weight of 15,000 or less, and that, when the bath contains 11%by weight of solids, the specific electroconductivity of the bath shouldbe controlled to 150-800 ,u /crn. (measured at 25 C.).

An electrodeposition coating material composed of a Water-soluble orwater dispersible resin capable of satisfying the abovernentionedconditions has an excellent onecoat finish property. For the purpose ofobtaining a resin component, which satisfies such conditions, monomersconstituting said resin will be examined below.

Generally, monomers having cross linking functional groups which displaythermosetting properties are mostly high in polarity and great in degreeof hydrophilic property. In order to obtain an electrodeposited filmhaving desired solvent resistance, stain resistance and anti-rustproperty, the cross linking density of the film should be made high. Forthe achievement of the above purpose, therefore, cross linkingfunctional monomers should be used in considerably large amounts.However, polymers obtained by using large amounts of said hydrophilicvinyl monomers are low in pKa value and high in n value, and hence arenot desirable. In order to improve the above points, it is necessarythat relatively vinyl monomers containing hydrophobic, cross linkingfunctional group be used to prepare polymers which have pKa, n, Tg andaverage molecular weight values within the aforesaid ranges and whichcan attain suitable cross linking densities. Generally, hydrophobiccross linking functional groups are relatively low incro ss linkingreactivity, but are advantageous in that in the heating step, they bringabout heat reflow prior to cross linking reaction to make it possible toform smooth coated surfaces.

Based on the above-mentioned viewpoints, the inventors examined resincapable of meeting the objects of the present invention to find that thepresent invention can be achieved by using as the coating resin acopolymer composed of 93.5-35 mole percent of a component (A), which isa monomer mixturejcomprising at least one monomer represented by thegeneral formula mmooon [IV] wherein m is 1 or 2; and 5-50 mole percentof a component (C), which is at least one compound represented by thegeneral formula H CH2=CCON I t \R;T OR3 [V] wherein R is as definedabove, R is a branched or straight chain alkylene group having 1-8carbon atoms, and R is a branched, cyclic or straight chain alkyl grouphaving 1-6 carbon atoms.

The compound represented by the general Formula III, which is used inthe present invention is an acrylate or methacrylate in which the alkylgroup represented by R is a methyl, ethyl, n-propyl, isopropyl, n-butyl,secondary butyl, tertiary butyl, pentyl, Z-ethylhexyl, monyl, decyl,dodecyl or stearyl group. 'In case the hardness of the resulting filmand the bath stability of the coating bath employed are to be taken intoconsideration, it is desirable to use, in a suitable combination, a longchain alkyl acrylate or methacrylate and a short chain alkyl acrylate ormethacrylate. The said other copolymerizable unsaturated monomer isstyrene, an ot-alkyl-substituted styrene derivative, acrylonitrile, or ahydroxyalkyl acrylate or methacrylate represented by the general formulaR l wherein R and R are as defined above. Concrete examples of saidhydroxyalkyl acrylates and methacrylates are those in which thehydroxyalkyl group is a Z-hydroxyethyl, Z-hydroxypropyl, Z-hydroxybutyl,Z-ethyl-Z-hydroxyethyl or l-hexyl-Z-hydroxyethyl group.

The above-mentioned component (A) is a monomer mixture constituting atrunk component of the high polymer, which is used as a component of thecoating composition. A particularly excellent coating composition forelectrodeposition coating can be obtained when there is used, as thecomponent (A), a monomer mixture prepared by mixing in a molar ratio of99.9/0.l to 40/60 a monomer represented by the general Formula III withother copolymerizable unsaturated monomer.

As carboxylic acids constituting the component (B), there may be used,in addition to the carboxylic acids represented by the general FormulaIV, acrylic, crotonic, fumaric and acids, and anhydrides of said acids.These acids, however, are inferior in copolymerizability with othermonomers employed, and therefore the use of said acids is not desirable.Polymers to be used in the electrodeposition coating methods arerequired to be uniform in structure and the like, particularly in pKavalue. If polymers having a wide pKa value distribution are used,polymers low in pKa value migrate or orient, with lapse of time, intothe aqueous phase, whereby not only the stability of the coating bath isinjured but also the properties of the resulting films are degraded. Itis therefore a required condition to use itaconic orot-methyleneglutaric acid, which is excellent in copolymerizability.

The above-mentioned acids not only play important roles to impartelectrophoretic properties to the coating material components but alsoare elements indispensable for dispersing the coating materialcomponents into an aqueous medium. They are important also as crosslinking reaction catalysts in the baking step of films. Further, in thecase of pigmented coating materials using pigments in combination, theydisplay effects of improving the affinity of the pigments for the resincomponents. However, the above-mentioned acids are hydrophiliccompounds, so that when used in large amounts, they bring about thedegradation in characteristics of the resin obtained and in physicalproperties of the resulting films. It is therefore desirable to use theacids in amounts of from 1.5 to 15 mole percent.

A great characteristic of the present invention resides in the use ofthe compounds represented by the general IFormula V. Typical as saidcompounds are acrylamides or methacrylamides in which, in theN-alkoxyalkyl group,

the N-alkoxy group represented by R 0- is a methoxy,

ethoxy, butoxy, n-propoxy, pentoxy or group, and the alkylene grouprepresented by R is a methylene, ethylene, propylene, hexylene or2-ethylhexylene group. These compounds are more hydrophobic crosslinking functional monomers than acrylamides, methacrylamides andN-methylol acrylamides or methacrylamides, and can be used inconsiderably large amounts without giving any detrimental effect to thepKa and n values of the resulting polymers. Further, they give filmshaving not only a desired cross linking density but also heatreflowability, and therefore glossy coated surfaces can be obtained.Among these monomers, N-butoxymethyl acrylamide and N-butoxymethylmethacrylamide can be said to be particularly preferable comonomers inthat not only they are excellent in copolymerizability with othermonomers and the resulting polymers are favorable in storage stability,but also they are prominent in affinity for pigments, melamine resinsand epoxy resins which are used in combination therewith. The amounts ofthese monomers employed are in the range of 5-50 mole percent,preferably 30 mole percent, when the pKa and n values of the resultingpolymers are taken into consideration.

For the preparation of polymers usable in the present invention, theaforesaid monomers may be polymerized, according to an ordinarypolymerization method, in an ordinary organic solvent in the presence ofdesired amounts of a radical polymerization catalyst and a molecularweight modifier. However, in case the dispersion stability in water ofthe resulting polymer and the stability with lapse of time of theaqueous bath are taken into consideration, the use of organic solventsmiscible with water is particularly desirable. As these organicsolvents, there are alcohols such as methanol, ethanol, butanol,propanol, and isopropyl alcohol; glycols such as ethylene glycol,propylene glycol, hexylene glycol, and diethylene glycol; Cellosolvessuch as methyl Cellosolve, ethyl Cellosolve, and butyl Cellosolve; oraqueous mixtures thereof. Great advantages attained by use of theabove-mentioned polymerization solvents are as mentioned below.

In the step of dispersing a polymer in water, it is not necessary toeffect such solvent substitution as in the case where a water-insolublepolymerization solvent has been used. Further, in case solventsubstitution has been effected, the resulting polymer itself has pKavalues of a certain range, in general, so that a polymer low in pKavalue tends to migrate into the aqueous phase. Accordingly, the polymeris lowered in stability during storage as a resin solution. In contrastthereto, in case a water-miscible organic solvent has been used, no suchsolvent substitution is necessary in the step of dispersing the polymerin water. Moreover, the polymer is stored in the organic solvent, andtherefore the dissolved state of the polymer does not vary to make itpossible to obtain an electrodeposition coating composition, which ismarkedly excellent in stability.

As the polymerization initiator to be used in the preparation of thepolymer, any of the ordinary radical polymerization initiators may beused. Examples of such polymerization initiator are benzoyl peroxide,cumene hydroperoxide, ditertiary butyl peroxide, azobisisobutyronitrile,and azobisisovaleronitrile. As the molecular weight modifier, there maybe used such mercaptan as tertiary dodecyl mercaptan, n-dodecylmercaptan, butyl mercaptan, or 2- mercaptoethanol.

In order to disperse the resulting copolymer in water, it is necessarythat the copolymer be neutralized. Neutralizing agents usable in theabove case are ammonia, primary amines, secondary amines, tertiaryamines, hydroxyalkylamines thereof, or salts thereof. However, theseneutralizing agents give adverse effects, depending on the degree ofhydrophilic properties thereof, on the pKa and n values of the polymers,and therefore care must be taken. I

For the preparation of the above-mentioned N-alkoxyalkylamide copolymerthere is thought of a process using isolated N-alkoxyalkyl acrylamidesor methacrylamides. In addition thereto, there are, as disclosed in US.Pat. No. 2,870,611 and British Pat. No. 1,115,130, the so-calledpolymer-modifying processes in which interpolymers having amide groupsor N-methylolamide groups are obtained using acrylamides,methacrylamide, N-methylolacrylamides or N-methylolmethacrylamides ascomonomers, and then the said amide groups are N-alkoxyalkylated by useof aldehydes and alcohols. However, according to the above-mentionedpolymer-modifying processes, hydrophilic groups are liable to remain.Further, the solvents employed are water-insoluble organic solvents, andtherefore the resulting polymer solutions should be subjected to solventsubstitution to bring about detrimental effects on the pKa and n valuesof the polymers. Moreover, the polymers are deteriorated in heatflowability and the electrodeposition coating baths are lowered in bathstability. According to the aforesaid processes, therefore, it isimpossible to obtain the present coating compositions forelectrodeposition coating which are suitable for one-coat finish andwhich have excellent filmforrning ability. Further, when the aboveprocesses are employed, it is necessary to add acid catalysts in orderto completely N-alkoxyalkylate the amide groups or N- methylolamidegroups contained in the polymers. These acid catalysts undesirably bringabout detrimental effects at the time of electrodeposition coating, andtherefore it is imposSible to obtain, according to said processes,electrodeposition coating materials suitable for one-coat finish.Accordingly, in order to obtain an electrodeposition coating material,it becomes an essential condition to use an N-alkoxyalkyl acrylamide ormethacrylamide as a comonomer. In this case, however, there arises agreat problem in that isolated N-alkoxy-alkyl acrylamide ormethacrylamide is expensive.

In view of the above, the present inventors examined processes forinexpensively preparing N-alkoxyalkyl acrylamides and methacrylamideswhich are used as comonomers. As the result, the inventors haveaccomplished the following two methods:

The first method is such that an N-alkylol acrylamide or methacrylamideis used as a starting material; a mixture comprising a lower aliphaticalcohol and an organic solvent azeotropic with water, or a vinyl monomerazeotropic with water, is used as a dehydrating agent; and theunsaturated acid (B), which is an essential component of the presentcomposition is used as a catalyst for N-alkoxyalkylation of theN-alkylol group.

The second method is such that acrylamide or methacrylamide is used as astarting material; a mixture or addition product of formaldehyde and alower aliphatic alcohol is used as a modifying agent for the amidegroup; and the same dehydrating agent and acid catalyst as in the firstmethod are used. According to said methods, a monomer mixture comprisingthe component (C) and the component (B) can be easily obtained byfeeding to the monomers a given amount of an acid catalyst, which is anelement indispensable in the present invention. Further, when a vinylmonomer azeotropic with water is used as the dehydrating agent, amonomer mixture comprising (A), (B) and (C) can be obtained with easeand at low cost. As the acid catalyst, a-methyleneglutaric or itaconicacid, which is useful also as a comonomer, is preferably used. As thesolvent for dehydration, an aromatic hydrocarbon such as benzene ortoluene, or a vinyl monomer such as acrylonitrile, displays prominenteffects.

The present coating compositions for electrodeposition coating are ofthe self-cross linking type and give films excellent in physicalproperties. However, in order to further improve the properties of theresulting films, such as hardness, corrosion resistance and the like, itis desirable that melamine resins or epoxy resins be used incombination. The improvement is achieved by blending 60 parts by weightor less of N-alkoxymethylmelamine and/ or epoxy resins with parts byweight of the resin component comprising 03.5 to 35 mole percent of thecomponent (A), 1.5 to mole percent of the component (B), and 5 to 50mole percent of the component (C). Usable as such melamine resins areN-alkoxymethyl melamines, preferably those in which the alkyl group ofthe alkoxymethyl group has 14 carbon atoms. Alternatively, these may beN-alkoxymethyl melamines in which the N- alkylol group has been left inpart. Usable as the epoxy resins are those having an epoxy equivalent of1002,000. These include, for example, condensation products ofpolyethylene glycol or polypropylene glycol with epichlorohydrin;triglycidyl isocyanurate; epoxy resins obtained from epichlorohydrin andBisphenol A; epoxidized resins; vinyl cyclohexene dioxide; diglycidylphthalate ester; and glycerine triglycidyl ether. These epoxy resinsdisplay great etfects particularly in that they can improve thecorrosion resistance of the resulting films. Further, these compoundsare ordinarily used in the form of solutions in suitable solvents, butmay also be used in the form of powders.

In order to disperse the polymer, obtained in the above manner, in anaqueous medium and to use the dispersion as an electrodeposition coatingbath, the specific electroconductivity of the bath at the time ofpreparation should be controlled to 150-800 ,u. /cm. (measured for 11%by weight of solids, measured at a bath temperature of 25 C.). If thespecific electroconductivity of the bath is more than 800 a /cm., theelectrodeposition of the coating material components onto the surface ofa metal to be coated becomes low in efficiency. When the specificelectroconductivity is less than 150 ,uU/Cm., the amount of coatingmaterial particles electrodeposited onto the surface of a metal to becoated increases, but, on the other hand, the degree of racking ofcoating material particles on to the surface of material to be coateddecreases to 0 bring about such undesirable phenomena that the adhesionbetween the resulting film and the material to be coated is lowered andthe solvent is left in the film. It is therefore desirable that thespecific electroconductivity of the electrodeposition coating bath beadjusted to 200- 600 ,uZj cm.

A polymer obtained according to an ordinary polymerization process is amass of polymers having considerably wide distributions of pKa, n andmolecular weight values. Therefore, in case the conventionalelectrodeposition coating material, which contains such a polymer asmentioned above, is used to form an electrodeposition bath, polymers lowin pKa value migrate into the aqueous phase with lapse of time, wherebythe whole system of the coating bath is lowered in apparent pH, and thespecific electroconductivity of the bath increases and, at the sametime, becomes closer to a definite value. Further, in the above process,there occur such phenomena as variation in dissolved state of coatingmaterial particles lack in the difference of electrophoretic migrationof the particles, and formation of precipitate. Owing to such variationof coating bath with lapse of time, the resulting film is undesirablydegraded in gloss and is deteriorated in physical properties due toincrease in film thickness.

It is the electrodeposition coating material of the present inventionthat has been developed in order to overcome such undesirable phenomenaas mentioned above. However, even in the case of an electrodepositioncoating bath prepared by using the present coating material, whichcontains thepolymer obtained under such strict condi-.

tions as above, there are observed such phenomena that the bath islowered in pH and is increased in specific electroconductivity whenallowed to stand for a long period of time after preparation, with theresult that the resulting film is degraded in gloss and deteriorated inphysical properties. Such phenomena are considered ascribable to thefact that water-soluble polymers low in pKa value orient and migrateinto the aqueous phase, as mentioned previously. When said water-solublepolymers, which have migrated into the aqueous phase, are

removed from the bath according to a dialysis process or a process usingion exchange compounds, e.g. ion exchange resins or membranes, the pHand specific electroconductivity of the bath can be brought back tosubstantially the same pH and specific electroconductivity values at thetime of preparation of the bath, whereby the gloss and properties of theresulting bath can be maintained constant.

In addition to the above process for the stabilization ofelectrodeposition coating bath by use of the ion exchange compounds,there is a method in which an amphoteric electrolyte capable of actingas a base in the vicinity of the pole of a material to be coated isadded to the electrodeposition coating bath, whereby the stability ofthe bath can be greatly improved. The phenomenon taking place in theabove method has not been clarified in detail, but is consideredaccountable to the mild deposition of coating material particles in thevicinity of the pole. Preferable as such amphoteric electrolyte arethose having an isoelectric point of 6.5-8.5, e.g. amino acids such asL-histidine, L-glycine, and the like. The bath stability can also beimproved by preventing the coating material particles from agglomerationin the aqueous medium, or by adding to the coating bath a nonionicsurface active agent effective for preventing polymers low in pKa valuefrom elution into the aqueous medium. As the nonionic surface activeagent, there may be used, for example, a copolymer of ethylene oxidewith propylene oxide. In case a high anti-rust property is desired to beimparted to the resulting film, an alkylamine, preferably awater-insoluble alkylamine, which can neutralize the acid groupcontained in the polymer, may be added during the curing of the film.The water-insoluble alkylamine includes n-butylamine, n-hexylamine,n-octylamine and laurylamine.

Electrodeposition coating materials, in which containing pigment haveheretofore been obtained by use of pigmented paste prepared byneutralizing a coating material to impart water dispersibility thereto,adding a pigment to the coating material, and then kneading theresulting mixture. However, the coating materials for electrodepositioncoating, which are obtained according to such a process as above,variously differ in stability in aqueous bath. Further, the developmentof coating materials excellent in dispersion stability hasconventionally been elfected in a mere trial and error manner, andprocesses for the analysis and solution of causes for said difference'in both stability have not yet been found.

In view of such actual state as mentioned above, the present inventorsmade studies, paying attention to the point that no matter how excellentresins for one-coat finish had been developed, the pigmented pastematerial having excellent characteristics and suitable for one coatfinish could not be obtained unless the characteristics of pigmentsemployed should also be taken into consideration. As the result, theinventors have found that a pigmented coating material forelectrodeposition coating which has excellent characteristics and whichis suitable for one-coat finish can be obtained by use of a resin which,after neutralization, shows such characteristics in the Formula I as8.0gpKa, 0.5 n 1.5 and 30% o 80%, and of a pigment which satisfies therelationship represented by the formula [pKp-pKa| 0.1 [VII] wherein pKpis the acidity of the pigment, and pKa is the acidity of the resin.

The dispersion stability of a coating material in an aqueous bathcontaining a pigment and a resin is greatly affected by the wettabilitybetween the resin and the pigment. 'In the present invention, the stepof coating the pigment with the resin is carried out in an organicsolvent, and it is considered that the wetting phenomenon be- PlHgO]RCOOH [VIII] wherein P[H O] represents a pigment having adsorptionwater, and RCOOH represents a carboxylic acid resin. Thus, thedispersion stability in water of the pigment, which has once beencoated, is greatly dominated by the characteristics of the resinemployed. It is considered that K in the process of the Formula VIII isproportional to the value of IpKppKa|, i.e. the difference between pKa,which represents the proton releasability of the carboxylic acid resin,and pKp, which represents the protondischarging force of P[H O]. Thegreater the value of |pKppKa[, the more firmly the pigment is coatedwith the resin, and the dispersibility of the resultant is comparable tothat of a resin containing no pigment, whereby the effect of using theresin suitable for one-coat finish and having excellent pKa and n valuescan also be displayed.

In case a pigment and a resin in such a relationship as pKp'= pKa areused, the wetting phenomenon according to the Formula VIII between thepigment and the resin becomes a markedly small value, and thewater-dispersibility of the pigment itself is also inhibited. It istherefore considered that the resulting aqueous bath is lowered indispersion stability and, at the same time, the pigment and the resintend to show difierent behaviors in the electrodeposition coating step,with the result that the properties of the resulting film are alsolowered. Accordingly, in order to obtain a pigmented coating material,which has excellent dispersion stability in water and which is suitablefor one-coat finish, it becomes necessary that the condition[pKppKa|z0.l be satisfied.

In the present invention, pKa is a value measured under the conditionsset forth below.

A water-insoluble pigment has an amphoteric property, and when thepigment is dispersed in an alkaline or acidic medium, it shows excellentdispersibility, whereas at about a neutral pH, the dispersibilitythereof becomes markedly low. In a dispersion at an alkaline pH, thepigment is negatively charged, and the pH lowers with increasing pigmentconcentration. Accordingly, OH- is adsorbed on the pigment surface, andthe pigment disperses according to the equilibrium equation K2 P(H2O) CZP(OI-I-) +H+ [IX] Wherein P is the pigment. Since the dispersibility ofthe pigment becomes higher with increasing P(OH"), there is establishedthe equation When pK is replaced by pKp, it is possible, in view of therelationship between the term log which represents the dispersibility ofthe pigment, and the pH of aqueous bath, to define pKp by the pH at thetime when the pigment initiates to disperse at the alkaline side. Whenthe pH at said time is measured, the value of pKp can be calculated.

As pigments usable in the present invention, there are inorganicpigments such as titanium oxide, red oxide, carbon black, cobalt blue,Ultramarine blue, Cerulean, manganese blue, mars violet, chromium oxide,cobalt chromium green, yellow iron oxide, cadmium yellow and barite; andorganic pigments such as Permanent Red 4R, Hansa Yellow andPhthalocyanine Blue. In addition thereto, any pigments may be used sofar as they are difiicultly soluble in water. However, the pigmentsshould be so selected as to necessarily satisfy the relationship|pKp-pKa[20.1.

The present coating compositions for electrodeposition coating can give,according to any of clear coating and colored enamel coating, not onlyfilms having excellent physical and chemical properties but also filmshaving white and light clear colors and having excellent surface gloss.

'In the present invention, the coating operations may be effected insuch a manner that electrodeposition coating is carried out ordinarilyat a voltage of 40-200 v., and the resulting film is washed with water,is dried, and is then baked at 250 C. for about 30 minutes.

The coating compositions of the present invention are extremelysignificant in that even in the case of chemically treated cold rolledsteel plates, which have heretofore been considered to be such thatfilms having excellent surface gloss and prominent properties aredifficultly formed on the surfaces thereof according toelectrodeposition coating method and by one-coat finish, the presentcoating compositions can form such excellent films as in the case ofcold rolled steel plates.

The present invention is illustrated in further detail below withreference to examples, in which all parts and percentages are by weight.

EXAMPLE 1 (A) Preparation of a monomer mixture comprising N-butoxymethyl acrylamide and itaconic acid:

The monomers shown below were charged into a threenecked flask fittedwith a stirrer, a decanter and a thermometer, and the mixture wasdehydration-condensed at 70-97" C. for 6 hours.

Parts Acrylamide 444 n-Butanol 760 Benzene 700 Itaconic acid 162.5 40%butanol solution of formaldehyde 538 Hydroquinone monomethylether 3.5

The decanter had previously been charged with benzene, and the time whenthe amount of effluent water had reached a given amount was deemed asthe terminal of the condensation reaction. The resulting product wasanalyzed according to gas chromatography to find that the conversion ofacrylamide to N-butoxyrnethyl acrylamide was 96.5%, 2,500 parts of thesaid product was charged with 1055 parts of isopropanol, and 1055 partswas distilled off as an azeotropic mixture of benzene with isopropanol.

(B) The monomers shown below were charged into the flask employed in(A), and a monomer mixture comprising N-butoxymethyl acrylamide anditaconic acid was obtained in the same manner as in (A) Parts N-methylolacrylamide 632 n-Butanol 1030 Benzene 703 Itaconic acid 162.5Hydroquinone monomethylether 3.5

The resulting product was analyzed according to gas chromatography tofind that the conversion of N-methylol acrylamide to N-butoxymethylacrylamide was 97.5%. 2,500 parts of the said product was charged with1055 parts of isopropanol, and benzene was distilled off as anazeotropic mixture with isopropanol.

(C) In the same manner as in (A), a monomer mixlure comprisingN-butoxymethyl acrylamide, itaconic acid and acrylonitrile was obtainedfrom the monomers shown below.

, l 7 Parts Acrylamide 444 40% butanol solution of formaldehyde 538Acrylonitrile 700 Itaconic acid 162.5 Hydroquinone monomethylether 3.5n-Butanol 760 I The resultingproduct was analyzed according to gaschromatography to find that the conversion of acrylamide toN-butox-ymethyl' acrylamide was 96.0%.

(D) In the same manner as in (A), a monomer mixture comprisingN-butoxymethyl acrylamide and methacrylic acid was obtained from themonomers shown below:

. 7 Parts .N-methylol acrylamide 632 n-Butanol 1030 Benzene 703Methacrylic acid 120 Hydroquinone monomethylether 3.5

The resulting product was'analyzed according to gas chromatography tofind that the conversion of N-methylol acrylamide'toN-butoxymethyl'acrylamide was 96.3%.

This product was carefully concentrated, and N-butoxymethyl acrylamidehaving a boiling point of 1l0-115 'C 1 mm. Hg was isolated, yield 85%.

(E) In the same manner-as in (A), a monomer mix- "ture comprisingN-butoxymethyl acrylamide and a-methyleneglutaric acid wasobtained fromthe monomers shown below: M e

v. 1 Parts Acrylamide fl; 444 ,40% butanol solution of formaldehyde 538'n-Butanol s 760 Benzene 700 -Methyleneglutaric acid-. 180 .Hydroquinonemonomethylether 3.5

The resulting productwas analyzed according to gas chromatography tofind that the conversion of acrylamide to N-butoxymethyl acrylamide was95.5%.

EXAMPLE 2 i The compounds shown below were charged into a four- .necked'flask fitted with a stirrer, a thermometer and a cooler,i,and themixture was polymerized in a nitrogen atmosphere at 68 C. for 6 hoursand then at 75 C. for I additional'2 hours. a

p Parts Ethyl acrylate 271 Styrene 166 N-butoxymethyl acrylamide 100.Itaconic acid 12.4 -2-mercaptoethanol 5.8 .Azobisisobutyronitrile. 24Isopropanol 427 The resulting copolyrner solution was neutralized byaddition of 6.65 parts of fl-dirnethylaminoethanol to obtain a resinoussolution having a solids content of 57.2

wt. percent, an acid number of9.8, Tg. of C., pKa of 8.7, n of 0.9 andon of 45%.:To 100 parts of this resin coating bath, a cold rolled steelplate, a zinc phosphatetreated steel plate, and an ferricphosphate-treated soft steel plate were individually subjected toelectrodeposition coating at a bath temperature of 25 C. for 3 minutesat 60 v. (distance between electrodes=40 mm.; cathode area/ anodearea=5/7). After water-washing and air-drying, the resulting films werebaked at 180 C. for 30 minutes. The efiiciencies of the thus formedfilms were as shown in Table 1.

TABLE 1 Substrate Cold Ferric Zine rolled phosphatephosphatesteeltreated treated Item plate plate plate Gloss value (60) 90. 5 89. 1 86.9 Thickness (p) 28 26 29 Pencil hardness. 2H 2H 2H Cross cut /100100/100 100/100 Solvent resistance:

4 4 4 4-5 4 4 5 5 5 5 5 5 Acid resistance 5 5 5 In the above table:

Gloss value was measured according to 60 mirror surface reflectionmethod.

Cross cut value was measured in such a manner that squares of 1 mm. inside were drawn with a needle on the surface of the film and were peeledoff by use of an adhesive tape, and the number of the remaining squareswas represented by percentage.

Solvent resistance was measured in such a manner that the film surfaceof the coated plate Was rubbed 20 times with a gauze impregnated withthe organic solvent, and the damaged degree of the film surface wasevaluated according to a S-grading system. The best value wasrepresented by 5, and the worst value by 1.

Alkali resistance was measured in such a manner that a spot of a 5%aqueous caustic soda solution was placed on the film surface of thecoated plate for 24 hours and the damaged degree of the film wasevaluated according to a S-grading system.

Acid resistance was measured in such a manner that a spot of a 5%aqueous hydrochloric acid solution was placed on the film surface of thecoated plate and the damaged degree of the film was evaluated accordingto a S-grading system.

Substrate was a cold rolled steel plate of 70 mm. x mm. x 0.8 mm., whichwas used either as such or after treatment with an anti-rust surfacetreating agent.

From the results shown in Table 1, it is evident that the films formedby use of the present coating composition is excellent not only in glossbut also in efliciencies and that the coating composition of the presentinvention is suitable for one-coat finish.

EXAMPLE 3 The compounds shown below were charged into the same device asin Example 2, and the mixture was polymerized for 12 hours in the samemanner as in Example 2 to obtain a resin solution.

Parts 2-ethylhexyl acrylate 806 Styrene 520 N-butoxyrnethylacrylamideitaconic acid mixture obtained in Example 103) 965 Itaconicacid 16.5 Azobisisobutyronitrile 59.0 Z-mercaptoethanol 22.5 Isopropanol763 To the thus obtained resin solution, 44.4 parts of B-dimethylaminoethanol was added to prepare a resin having Tg of -9 C.,pKa of 9.20, n of 1.17, and a of 40%, 100 parts of this resin solutionwas charged with 75 parts of titanium dioxide having pKp of 906, and themixture was ground in a ball mill for 24 hours. The mixture was furthercharged with 200 parts of the resin solution and was ground to obtain awhite pigmented paste. This enamel paste was used to prepare anelectrodeposition coating bath having a solids concentration of 13%, apH of 9.02 and a specific electroconductivity of 2.24X p13 cm. (at thetime when the solid content was 11%). Using the thus prepared coatingbath, a cold rolled steel plate, a zinc phosphate-treated steel plateand an ferric phosphate-treated steel plate were individually subjectedto electrodeposition coating at a bath temperature of 25 C. for 3minutes at 80 v. under the same electrode conditions as in Example 2.After water-washing and airdrying, the resulting films were baked at 180C. for

films having excellent efficiencies. In Table 3, (Exc) in the column17th day shows that an ion exchange method was applied on the 17th day.When an electrodeposition coating bath is allowed to stand for aconsiderably long period of time, the elution of water-soluble polymerstakes place to lower the pH of the bath and to increase the specificelectroconductivity thereof, whereby the resulting film is deterioratedin efficiencies. If, in this case, the water-soluble polymers elutedinto the bath are removed by means of an ion exchange resin, the bathcan be restored to a bath which is high in stability and which can givea film excellent in efiiciencies, as is clear from Table 3.

EXAMPLE 4 30 minutes. The efiiciencies of the thus formed films were Amixture comprising the compounds Shown below was as shown Tablepolymerized under the same conditions as in Example 3,

TABLE 2 and was neutralized with 17.8 parts of B-dimethylaminosubstrateethanol to obtain a resin solution having a solids content C01 d FerricZinc 20 of 57.2%, an acid number of 19.6, and a viscosity of rolledphosphatephosphate- U (Gardner).

ste treated treated Parts Item plate plate i 2-ethylhexyl acrylate 276Glossvaluo 86.3 86.5 Styrene 207 g rii fi ii ii ls's'jj" I r 1 i? r t?2-hydroxyethyl methacrylate 31.3 ggf fg f 100/100 loo/10 100/100N-butoxymethyl acrylamide-itaconic acid mixture a 5-4 54 obtained inExample 1(B) 389 g g g Itaconic acid 6.5 5 5 5 Isopropanol 312 3 3 3? g;Azobisisobutyronitrile 22.4 Impact resistance (cm.) 50 50 50Z-mercaptoethanol 6 Bending test (mm.) 2 Saltspraytcst The thus obtainedresin had Tg of -1.5 (3., pKa, of 8.73, n of 1.15, and a of 40%. Theresin solution was 111 Table other items than iIIIPEW'E resistance,bending treated in the same manner as in Example 3 to obtain a test andSalt p y test are the Same as in Table white pigmented paste. This pastewas used to prepare Impact resistance Was measured in Such a manner thata coating bath having a solids concentration of 13%, a onto the filmsurface, an iron hammer having a diameter PH f 5 and a ifielectroconductivity f 357x102 of 1% inch and a Weight of 500 WasVertically pp #0 /cm. (at the time when the solids content was 11% froma Certain height, and impact resistance of the Subsequently,electrodeposition coating and baking were film was represented by theheight of the iron core at the 40 effected under the Same conditions asin Example The time h the film 'f had been damaged efliciencies of theresulting films were as shown in Table 4.

Bending test was carried out in such a manner that a core of steel rodhaving a diameter of x mm. was disposed on the back side of the coatedsteel sheet and the steel plate was bent to an angle of 360. The resultof the bend- TABLE 4 ing test was represented by the diameter of a coreof steel rod at the time when the film surface had been damagedsubstrate by said test. Coiled Ferric Zinc Salt spray test was carriedout in such a manner that the 2%? gg gi i g gg film was lineally cut toform a lineally cut portion on the tem plate plat plate film surface andwas sprayed with a 5% aqueous sodium 8&2 8Z2 chloride solution at 40 C.for 48 hours, and then the 2 I gs cut portion was peeled off by use ofan adhesive tape. Cross out jjjj 100/100 100/100 The result of the saltspray test was represented by the Solvent resistance: H 4 5 4P5 width ofpeeled film at the time when the film had been peeled. 4 5 5 5 Thevariations with lapse of time of coating baths 011- 5 4 4 tained in theabove manner were observed on the basis tained in the above manner abovemanner wree observed of gloss values of the resulting films. The resultswere as 0 shown in Table 3.

TABLE 3 Elapsed days Substrate 0 13 17 17 (Exe) 25 Colled rolled steelplate 84.1 76.5 i g i n t z giiii s p l ti t r2i$$liifjI: I 70.5 69.176.3

- q 2 2 5. i0 4. 33x10 5.90X101 iifir fiiiiiifii ffifi wi lffi'fiffi:582 16 8.90

As is clear from the results set forth in Table 3, the EXAMPLE 5 coatingcompositions of the present invention are favor able in bath stability,and the baths prepared by use of the present coating compositions cangive, even when A mixture comprising the compounds shown below waspolymerized under the same conditionsas in Example 3, and wasneutralized with 17.8 parts of fi-dimethylallowed to stand for aconsiderably long period of time, aminoethanol to obtain a resinsolution having a solids 17 content of 57.5%, a viscosity of Q(Gardner), and an acid number of 19.9.

The resin obtained had Tg of '-23.5 C., pKa of 8.79, n of 1.11, and onof 40%. The resin solution was treated in the same manner as in Example3 to form a white pigmented paste. This paste was used to prepare anelectrodeposition coating bath having a solids concentration of 13%, apH of 8.70, and a specific electroconductivity of 2.53 10 6 /cm. (at thetime when the solids content was 11%). Subsequently, electrodepositioncoating and baking were effected under the same conditions as in Example3.

On the other hand, an aqueous solution containing 0.01 mol/l. ofL-histidine was prepared and was adjusted to the same pH as that of theaforesaid electrodeposition coating bath. 50 g. of said aqueous solutionwas incorporated into 500 g. of the aforesaid coating bath to prepareanother coating bath. The thus prepared two baths were individuallysubjected to tests with continuous stirring in open at 25 C. The resultsare shown in Table 5 by way of variations in gloss value and thicknessof the resulting films.

TABLE 5 No Initially Incorporated T t incorporation incorporated after20 days 55 days Gloss Thickness Gloss Thickness Gloss Thickness lliOTE:Test plate employed was a zinc phosphate-treated l) a e.

As is clear from the above table, the bath which has not beenincorporated with the L-histidine solution is greatly lowered instability as compared with the bath incorporated therewith. Further, thestability of a bath lowered in stability is improved by incorporation ofthe L-histidine solution in an amount equal to that of the bath.

EXAMPLE 6 This example shows the case where a long chain acrylate wasused in combination with a short chain acrylate in order to impart heatflowability to the resulting film.

A mixture comprising the compounds shown below was polymerized under thesame conditions as in Example 3, and was neutralized with 44.4 parts ofB-dimethylarninoethanol to obtain a resin solution having a solidscontent of 57.7%, a viscosity of U (Gardner), and an acid number of19.3.

The thus obtained resin had Tg of 20 C., pKa of 9.15, n of 1.18, and aof 40%. The resin was treated in the same manner as in Example 3 to forma white pigmented paste. This paste was used to prepare anelectrodeposition coating bath having a solids content of 13%, a pH of8.90,

and a specific electroconductivity of 2.35 X 10 U/cnmat the time whenthe solids content was 11% Subsequently, electrodeposition coating andbaking were elfected under the same conditions as in Example 3. Theefiiciencies of the resulting films were as shown in Table 6.

TABLE 6 S ubstrate Colled Ferric 25?. rolled phosphatephosphatesteeltreated treated Item plate plate plate Gloss value 85.3 85. 5 4. 1Thickness (p) 37 39 8 Pencil hardness F-H F-H F-H Cross cut 100 100/100100/ 100 Solvent resistance" yl 5 5 5 g g 5 Alkali resistance I: 5 5 5Acid resistance 5 5 5 EXAMPLE 7 This example shows the fact that evenwhen a monomer mixture synthesized by use of acrylonitrile as anazeotropic dehydrating agent is used, films excellent in etlicienciesare obtainable.

A mixture comprising the compounds shown below was polymerized in thesame manner as in Example 3 and was neutralized with 8.9 parts of/3-diethylaminoethanol to obtain a resin solution having a solidscontent of 59.6%, a viscosity of Y (Gardner), and an acid number of10.5.

Parts Z-ethylhexyl acrylate 340 Styrene 234 N-butoxymethylacrylamide-itaconic acid-acrylonitrile mixture obtained in Example 1 (C)200 Itaconic acid 3.25 Azobisisobutyronitrile 22.5 Z-mercaptoethanol 6[[sopropanol 332.3

The resulting resin had Tg of -1.5 (3., pKa of 8.7, n of 1.19, and or of40%. The resin solution was treated in the same manner as in Example 3to obtain a white pigmented paste. This paste was used to prepare anelectrodeposition coating bath having a solids content of 13%, a pH of8.5, and a specific electroconductivity of 3.l3 10 /cm. (at the timewhen the solids content was 11%). Subsequently, electrodepositioncoating and baking were effected under the same conditions as in Example3. The efliciencies of the resulting films were as shown in Table 7.

This example shows the fact that even when a monomer mixture issynthesized from an acrylamide of N- butoxymethyl acrylamide, afavorable resin for electrodeposition coating can be obtained.

Into the same device as in Example 2 were charged 50 parts ofazobisisobutyronitrile, 10 parts of 2-rnercaptoethanol, and a mixturecomprising the compounds shown below.

Parts Ethyl acrylate 693 Styrene 426 N-butoxymethyl acrylamideitaconicacid mixture obtained in Example 1 (A) 486 Isopropanol 800 The resultingmixture was elevated in temperature in 2 hours. In this case, 5 parts of2-mercaptoethanol and 3 parts of azobisisobutyronitrile were added, andthe mixture was maintained at 68 C. After 2 hours, 3 parts ofazobisisobutyronitrile was added, and the heating was continued foradditional 2 hours. At the 6th hours from the beginning, the temperaturewas elevated to 75 C. and polymerization was effected for additional 2hours. The resulting solution was neutralized by addition of 17.8 partsof B-dimethylaminoethanol to obtain a resin solution having a solidscontent of 54.3%, a viscosity of R (Gardner), and an acid number of 9.8.This resin Tg of 17.5 C., pKa of 9.0, n of 0.88, and 0c of 40%. Theresin solution was treated in the same manner as in Example 3 to obtaina white pigmented paste. This paste was used to prepare anelectrodeposition coating bath having a solids concentration of 13%, apH of 8.55, and a specific electroconductivity of 2.50 10 g/cm. (at thetime when the solids content was 11%). Subsequently, electrodepositionand baking were effected under the same conditions as in Example 3. Theefiiciencies of the resulting films were as shown in Table 8.

This example shows the fact that if the resin employed is excessivelyhigh in Tg (glass transition temperature), no excellent film isobtainable.

A mixture comprising the compounds shown below was polymerized accordingto the process of Example 3 and was neutralized with 14.2 parts offi-dimethylaminoethanol to obtain a resin solution having a solidscontent of 56.5%, a viscosity of Z (Gardner), and an acid number of19.3.

Parts Ethyl acrylate 50 Methyl methacrylate 50 Styrene 395N-butoxymethyl acrylamide 78.5 Itaconic acid 26 Azobisisobutyronitrile22.4 Z-mercaptoethanol 6 Isopropanol 372 This resin had Tg of 84 C., pKaof 8.60, n of 0.95, and u of 40%. The resin solution was treated in thesame manner as in Example 3 to obtain a white pigmented paste. Thispaste was used to prepare an electrodeposition coating bath having asolids concentration of 13%, a pH of 8.8, and a specificelectroconductivity of 4.9 10 #0 /cm. (at the time when the solidscontent was 11% Subsequently, electrodeposition coating and baking wereeffected under the same conditions as in Example 3. The efficiencies ofthe resulting films were as shown in 20 Table 9, but the films had nosmoothness and were low in throwing power.

A mixture comprising the compounds shown below was polymerized accordingto the process of Example 3 and was neutralized with 44.4 parts ofB-dimethylaminoethanol to obtain a resin solution having a solidscontent of 56.8% and an acid number of 19.5.

Parts 2-ethylhexyl acrylate 806 Styrene 520 N-butoxymethyl acrylamide400 wMethyleneglutaric acid Azobisisobutyronitrile 59 Z-merceptoethanol22.5 Isopropanol 753 The resin obtained had Tg of --8.0 C., pKa of 9.25,n of 1.15, and a of 40%. This resin was treated in the same manner as inExample 3 to obtain a white pigmented paste. This paste was used toprepare an electrodeposition coating bath having a solids content of13%, a pH of 9.0, and a specific electroconductivity of 2.13 10 13 /cm.(at the time when the solids content was 11%). Subsequently,electrodeposition coating and baking were effected under the sameconditions as in Example 3. The efliciencies of the resulting films wereas shown in Table 10. As is clear from the results set forth in thetable, the use of a-methyleneglutaric acid also results in filmssubstantially the same in efficiencies as in the case where itaconicacid is used.

TABLE 10 Substrate Colled Ferric Zinc rolled phosphatephosphatesteeltreated treated Item plate plate plate Gloss value 85. 5 84. 7 83. 8Thickness (a) 4 39 39 Pencil hardness F-H F-H F-H Cross cut /100 100/100100/100 Solvent resistant:

ylene 5 5 5 Isopropanol" 5 5 5 eetone 5 5 5 Alkali resistance.-. 5 5 5Acid resistance- 5 5 5 EXAMPLE 1 1 To 375 parts of the white pigmentedpaste obtained in Example 3 was added 30 parts of an epoxy resin havinga melting point of 64-74 C., an epoxy equivalent of 450-500, and amolecular weight of about 900 (which was a condensation product ofbisphenol A with polyethylene glycol and was used in the form of a 50%butyl Cellosolve solution). After ground, the mixture was used toprepare an electrodeposition coating bath having a solids concentrationof 13.2%, a pH of 8.66, and a specific electro-conductivity of 3.02 10m; /cm. (at the time when the solids content was 11%). Using the thusprepared electrodeposition coating bath, an ferric phosphate-treatedsteel plate and a zinc phosphate-treated steel plate were 21 subjectedto electrodeposition coating at 80 v. for 3 minutes. Subsequently, theresulting films were baked at 180 C. for 30 minutes. The efiiciencies ofthe films were as shown in Table 11.

22 In the table, Gloss [I] is the gloss value of the film formed byeffecting the electrodeposition coating immediately after preparation ofthe bath, and Gloss [II] is the gloss value of the film obtained byeffecting the TABLE 11 5 electrodeposition coating after continuouslystirring the bath at 40 C. for 7 days after preparation. i fl From theresults set forth in Table 13, it is understood Ferric Zinc that,depending on the difference in molecular weight, the ifgt g f g gpolymers differ in pKa and n values, though monomers Item plate late 10constituting the polymers are same, and the stability ofelectrodeposition coating baths prepared therefrom and l t jfl l s dls:32 35 the gloss of the resulting films are greatly affected. It is gs sei ii 100/100 100 63 also understood that particularly when a polymerhigh in Solvent resistance: molecular weight is used, no film excellentin gloss can g fgga g g g be o ained because the resin is decreased inpKa value, Acetone 5 5 is increased 1n 11 value and is made inferior inbath fil l rgn r egl sggg e fl g g stability, and the resulting film isdegraded in heat re- Salt spray test (51311 .I1III I-I II 4. 5 l. 5flowability.

EXAMPLE 14 AS IS from the Salt Spray .results.set forth. In Each 2 g. ofthe pigments set forth in Table 14 were Table 2, it is understood thatacrylic coating materials containing epoxy resins increase the corrosionresistance mdmdulmy dlspersed m 100 of Water dispersions of theresulting films were ad usted to the pl lwalues as shown 1n Table 14.After 3 hours, the precipitated volumes of the pigments EXAMPLE 12 weremeasured, and the pKp values of the pigments were To 100 parts of theresinous solution obtained in Excalculated by aforesald relatlonshlp(page ample 4 was added 10 parts of water-soluble melamine- TABLE 14resin. This mixed resinous solution was treated in the same manner as inExample 3 to obtain a white pigmented paste. This paste was used toprepare a coating bath having a solid concentration of 13 weightpercent, a pH of 8.9, and a specific electroconductivity of 3.15 X10 0.B/cm. (at the time when the solid content was 11 weight percent).

Subsequently, electrodeposition coating and baking were efiected underthe same conditions as in Example 3. The efiiciencies of the resultingfilms were as shown in Table 12.

TABLE 12 Substrate Colled Ferric Zinc g fi ig mii iggfig Of the pigmentsshown in Table 14, TiO (R-SSO) is Item plate plate plate a product ofIshihara Sangyo K.K., and Carbon Black 8 84.7 83.3 5 is a product ofMitsubishi Kasei K.K.

32 32 2s The precipitated volume referred to in the above is thecrosscut ,ggggg 3,35}, 5, 33 v l m represen ed by percent, of a pigmentor enamel Solvent resistance: which has precipitated after dispersing itin water at a figg 5 g g certain pH and allowing the dispersion to standfor a Acetone... 5 5 5 definite period of time. The greater the saidvalue, the 3 553 ,5533 g g f; more favorable the water dispersibility.

Plgmented pastes were obtained by use of resins having pKa values of8.33 and 9.06 and pigments havin the Kp EXAMPLE 13 values shown in Table15. These pastes were usgd to pre- Electrodeposition coating baths wereprepared in the pare coating baths. The thus prepared pgimented bathssame manner as in Example 3, except that the amount were measured indispersion stability to obtain the re of the Z-mercaptoethanol, whichhad been used as a mosults shown in Table 15. lecular weight modifier,was varied as shown in Table 13. Using the thus prepared coating baths,colled rolled steel TABLE 15 plates were sub ected to electrodepositioncoat-mg at 80 P pm d I v. for 3 minutes. Subsequently, the resultingfilms were 1 1 baked at 180 C. for 30 minutes. The efficiencies of the fme after pKa of l t h films were as shown in Table 13. Resin Pigment 1.5hours 3hours Resin Pigment volume 8.33 9. 70 72. 5 55. 5 9. 06 9. 70 95TABLE 13 3.33 9.05 71.5 50.5 9.06 9. 53 73 8.33 8.60 22. 0 ll. 0 9. 0s9. 45 61 Amount of Z-mercapto- 8. 33 8. 30 10. 0 10. 0 9. 06 8. 95 52ethanol added 1 8.33 7.75 33. 0 11.0 9. 06 s. 00 52 8.33 6. 73 90. 0 99.0 9. 06 7. 75 54 1.25% 0.83% 0.42% 9.06 5.73 84 40 From the resultsshown in Table 15, it is clear that a 63.2 coating bath obtained bycombining a pigment and a resin 3 3 which satisfy the condition|pKppKa[;O.1 is excellent in water dispersibility of paint particles andis prominent Based the mixture' in dispersion stability thereof, aswell.

23 EXAMPLE 1s The resin having pKa of 9.20, which was obtained inExample 3, titanium oxide having pKp of 9.53, and carbon black havingpKp of at least were used to prepare colored coating baths in thefollowing manner. Grey pigmented bath:

To 100 parts of the resin solution, 55 parts of TiO and 1.5 parts ofcarbon black were added. The mixture was ground in a ball mill for 24hours and was then charged with additional 200 parts of the resinsolution to obtain a grey pigmented paste. This paste was used toprepare a coating bath having a concentration of 13% and a pH of 8.75.Black pigmented bath:

To 100 parts of the resin solution, 5.1 parts of the carbon black wasadded. The mixture was ground in a ball mill for 24 hours and was thencharged with additional 200 parts of the resin solution to obtain ablack pigmented paste. This paste was used to prepare a coating bathhaving a concentration of 11.8% and a pH of 8.8.

By use of the above-mentioned baths, colled rolled steel plates and zincphosphate-treated plates were electrodeposition-coated at 8 v. for 2minutes, and the resulting films were baked at 180 C. for minutes. Theefficiencies of the films were as shown in Table 16.

TABLE 16 Colored enamel Grey Black Colled Zine Zinc rolled phosphate-Colled phosphatesteel treated rolled treated Substrate plate plate steelplate plate Item:

Gloss value 75. 1 71. 8 87. 2 86. 6 Thickness (u) 30 32 49 36 Pencilhardness HB HB 3B 2B Cross eut 100/100 100/100 100/100 100/100 Solventresistance:

Xylene 45 4-5 5 4-5 Isopropanol 5 4-5 4-5 4-5 Acetone 5 5 4-5 4-5 Alkaliresistance 5 5 5 5 Acid resistance 5 5 5 5 From the results set forth inTable 16, it is obvious that even formed into colored coatings, thecoating compositions of the present invention give excellent films byone-coat finish.

The stabilities of the above coating baths are shown in Table 17 withreference to the gloss values of the films.

TABLE 17 Colored enamel Grey Black Colled Zine Colled Zinc rolledphosphaterolled phosphatesteel treated steel treated Substrate plateplate plate plate Elapsed days:

From the results set forth in Table 17, it is evident that the coloredenamel coating baths in accordance with the present invention aremarkedly excellent in stability and always give uniform films.

Referential Example 1 A mixture comprising the compounds shown below waspolymerized in the same manner as in Example 2 to obtain a resinsolution.

The resin solution was neutralized with 16 parts of 3-dimethylaminoethanol to form a resin having pKa of 8.57, n of 1.10, a of60%, and Tg of 3.0 C. The resin solution had a solids content of 54.0%,an acid number of 11.8, and a viscosity of T (Gardner). From the saidresin solution, a. white pigmented paste was obtained in the same manneras in Example 3. This enamel paste was used to prepare anelectrodeposition coating bath having a solids concentration of 13%, apH of 8.4 and a specific electroconductivity of 4.85 10 t; /cm. (at thetime when the solids content was 11%). Subsequently, electrorepositioncoating was effected under the same conditions as in Example 3, and theresulting films were baked at 180 C. for 30 minutes. The efficiencies ofthe thus formed films were as shown in Table 18.

TABLE 18 Substrate Colled Ferric Zine rolled phosphatephosphatestetreated treated Item plate plate plate Gloss value 78. 0 77. 6 67.3Thickness 04)-... 28 27 27 Pencil hardness. H H H Cross cut /100 100/100100/100 Solvent resistance:

Xylene 3 4 3 Isopropanol.. 4 5 5 Acetone 4-5 5 4 Alkali resistance 5 4Acid resistance 5 4 4 Bath stability test:

Gloss value at the 2nd day.- 18.7 13.2 43.1 Gloss value at the 7th day.14. 3 7.0 32.0

In the table, other items than the bath stability test are the same asin the case of Example 3. The bath stability test is represented by thegloss value of a film formed by subjecting the bath to continuousstirring in open at 25 C. and electrodeposition-coating the film duringsaid stirring. From the results set forth in Table 18, it is clear thatwhen acrylic acid is used, the resulting resin is favorable in pKa and nvalues, but a coating bath made by use of said resin is marked indegradation in stability due to elapse of time. This indicates the factthat then a polymer obtained by use of acrylic acid as the acidcomponent is the mixture of polymers having a various pKa value, so thatpolymers low in pKa value have gradually migrated into the aqueousphase.

Referential Example 2 An electrodeposition coating material was preparedby use of a polymer obtained in such a manner that an amide polymer wasformer by use of acrylic acid as an afiethylenically unsaturated fattyacid and then the amide group was N-butoxymethylated with formaldehydeand butanol. The results of examination in efiiciencies of theelectrodeposition coating material are shown in Table 18.

One half of a mixture comprising the compounds shown below was chargedinto the same device as in Example 2, and polymerization was initiatedat the boiling point of the mixture. The remaining mixture was addeddropwise in 3 hours and was polymerized.

To the resulting polymer solution, 121.5 parts of paraformaldehyde wasadded, and the mixture was dehydrated, with reflux, until water had beencompletely removed. The amount of water removed was 59.4 ml.

The thus obtained resin solution was charged with TiO and was treated inthe same manner as in Example 3 to prepare an electrodeposition coatingbath having a solids concentration of about a pH of 8.58, a specificelectroconductivity of 6.l7 10'-6,u/crn., pKa of 8.53, n of 0.74 and onof 40%.

The resin of the present invention, formed by using itacouic acid as theacid component (the resin obtained in Example 3), had pKa of 9.20 and nof 1.17, and gave a coating bath having a specific electroconductivityof 2.24X 10 U/cm. In view of the above, it is anticipated that the bathstability of a coating bath, which has been prepared by use of a polymerobtained by using acrylic acid as the acid component, would be such thatthe resulting films are inferior in efliciencies. This in consideredascribable to the fact that acrylic acid, when used as the acidcomponent, is low in copolymerizability with other monomers and givesthe mixture of polymers having various difierent pKa and n values, sothat polymers low in pKa value elute into the aqueous medium to degradethe stability of the coating bath.

Using the thus prepared coating bath, a colled rolled steel plate(abbreviated as Fe), a zinc phosphate-treated plate (abbreviated asP-Zn), and a ferric phosphatetreated plate (abbreviated as P-Fe) wereindividually subjected to (A) coating at 60 v. for 3 minutes and curingat 160 C. for minutes, (B) coating at 80 v. for 3 minutes and curing at180 C. for 30 minutes, and (C) coating at 100 v. for 3 minutes andcuring at 180 C. for 30 minutes. The efiiciencies of the resulting filmswere as shown in Table 19.

Referential Example 3 A mixture comprising the compounds shown below wastreated in the same manner as in Example 3 to obtain a resin solution.

450 parts of the resin solution was charged with 22.5 parts ofparaformaldehyde and 2.25 parts of triethylamine, and was refluxed tointroduce N-methylol group into the amide copolymer. The resin solutionis then treated in the same manner as in Example 3 to obtain a pigmentedpaste. This paste was used to prepare an electrodeposition coating bathhaving pKa of 8. 61, n of 0.42, a of a pH of 9.1, and a specificelectroconductivity of 7.43 10 ,,z;/cm. Using the thus prepared bath, acolled rolled steel plate, a zinc phosphate-treated plate, and a ferricphosphate-treated plate were individu ally electrodeposition-coated at66 v. for 3 minutes, and the resulting films were baked at 175 C. for 30minutes. The efiiciencies of the films thus formed were shown in Table21.

From the results set forth in Table 19, it is evident that films formedby use of the coating material of this referential example are not soexcellent in gloss and are also low in 'Erichsen value and impactresistance as compared with films formed by use of the present coatingcompositions.

Further, the stability of the above coating bath is shown in Table 20with reference to the gloss values of films formed by effecting thecoating at 60 v. for 3 minutes and the curing at 180 C. for 30 minutes.

TABLE 20 Substrate Coiled Ferric Zinc Specific rolledphosphatephosphateelectrocutieel treated treated ductivity Elapsed daysplate plate plate pH lls/cm.

From the results set forth in Table 20, it is understood that a coatingmaterial obtained by use of acrylic acid as the acid component ismarkedly low in bath stability, and is not usable as anelectrodeposition coating material, which is suitable for one-coatfinish and which has practical efliciencies.

TABLE 21 Substrate Coiled Ferric Zinc rolled phosphate phosphatesteeltreated treated Item plate plate plate Gloss value 1.0 1. 4 1. 0Thickness (l 60 60 50 Pencil hardnes F H Cross cut-- 20/100 /100 100/100Solvent resistance:

one 5 2 3 IsopropanoL. 5 2 4-5 Acet0ne 3 1 1 Alkali resistance. 3 3 3Acid resistance" 3 3 3 From the results set forth in Table 21, it isevident that the electrodeposition coating material of this referentialexample has no practical efliciencies, and is not suitable as a coatingmaterial for one-coat 'finish.

Referential Example 4 A mixture comprising the compounds shown below wastreated in the same manner as in Example 3 to prepare anelectrodeposition coating bath having pKa of 6.84, n of 2.21, a of 40%,a pH of 6.52, and a specific electroconducti vity of 1.28 X l-Ofim/cm.

Parts In this referential example, the resin D-l, in which Ethylacrylate 425 the copolymerization proportion of acid had been made Acrylamide 25 large to increase the acid number of the polymer, and Itaconicacid 50 the resin D-2 of the present invention, in which theAzobisisobutylonitrile 22.4 5 copolymerization proportion of acid hadbeen made 2-mercapto ethanol 6 small, were used to examine thecharacteristics of the Isopropanol 472 resins and the effects of saidresins on films obtained Using the thus prepared bath, a coiled rolledsteel plate, f P m p fl g Z a zinc phosphate-treated plate, and a ferricphosphate- 10 f th 2 e q g 5 9 c e vslue treated plate were individuallyelectrodeposition-coated to ig a i g si f z l 3 form films having,respectively, gloss values of 86.5, 28.0 g gd j i of Coatine bath hptherefrom and 83.5 and thicknesses of 47, 34.5 and 47. However, no ithat fil gbt'ained b :lectrode film having practical efliciencies couldbe obtained at all, ticlm coating is increased inntlhickness degradfd insmce the resm m the bat}? was a thermoplasnc smoothness and gloss. It isthus evident that the increase Referential Example 5 in acid number ofthe resin employed makes it impossible Mixtures and comprisingrespectively, the to obta n an electrodeposition coating materialsuitable compounds shown below were treated in the same manner forone'ccfat fimsh' We claim: as in Example 3 to obtain resin solutlons. 1.An aqueous coating composition for electrodeposr- D4: Parts tion coatingconsisting essentially of in water a watery acrylate 250 soluble orwater-dispersible copolymer resin comprising Styrene 143 93.5 to 35 molepercent of component (A), which is Q Y F W acrylamlde 286 a monomermixture of at least one compound represented itaconlc i by the generalformula: sopropano Azobisisobutyronitrile 22.4 000 2-mercaptoethanol 6.0R (I) D-2: wherein R is a hydrogen atom or a methyl group, and -Ethylacrylate 693 R is a branched or straight chain alkyl group havingStyrene 42 6 1-18 carbon atoms, with at least one other monomerN-butoxymethyl acrylamide-itaconic acid mixwhich is styrene, ot-alkylstyrene, acrylonitrile or a hyture in Example 1(A) 48 6 droxyalkylacrylate or methacrylate of the formula: P 9B 800 CH;=CCOOR OHAzobisisobutyronitrlle 5 6 I Z-mercaptoethanol .15 R l wherein R ishydrogen or methyl and R is a kylene of dz g g g fig g z z fiz g g fz igf 1-8 carbon atoms, wherein the component (A) is selected Ph Sicalcoistants of the esin nd i 3 6 so that the molar ratio of the monomerrepresented by the as Zhown in Table 22 r S a e C 1 g a s were 40general Formula I to said other monomer is 99.9/0.l to 40/60, 1.5-15mole percent of a component (B), which TABLE 22 is a compoundrepresented by the general formula:

Resin 011,:0-(30011 D-l D-2 (HflmCOOH (II) m, 7,75 9,06 wherein m is 1or 2, and 5-50 mole percent of a com- -23 pound (C), which is at leastone compound represented 72. 5 19, 0 by the general formula:Electrochemical equivalent 1, 260 6, 750 H n slpfeiffigeleotroconductivity of bath, tU/em 9 34 7 ltg 1 96 8 18 0 g\g,o 22 15 F?C0 N R RzoRg Using the said coating baths, colled rolled steel plates,wherein R is an defined above, R is a branched or ferricphosphate-treated plates, and zinc phosphatestraight chain alkylenegroup having 1-8 carbon atoms, treated plates were individuallyelectrodeposition-coated and R is a branched, cyclic or straight chainalkyl group to form films. The eificiencies of the filims were as shownhaving 1-6 carbon atoms, and wherein the sum of the in Table 23. abovecomponents (A), (B), and (C) is selected so TABLE 23 Resin Collcd ZincFerric Coiled Zinc Ferric rolled phosphatephosphaterolledphosphatephosphatesteel treated treated steel treated treated Substrateplate plate plate plate plate plate Item:

Gloss value 4s. 2 10. 3 13. 2 92.8 91. 3 00.8 Thickness 30 71 30 35 3sPencil hardness. F F F H H H Cross cut /100 100/100 100/100 100/100100/100 100/100 Solvent resistane Xylene 3 3 3 3 3 3 Isopropanol 4 4 4 43 4 Acetone 2 2 2 459 4 5 Alkali resistance 4 4 4 5 5 5 Acid resistance5 5 5 5 4 4 Film surface Coarse Coarse Coarse Smooth Smooth Smooth as tobe equal to 100 mole percent and characterized in that the resin afterneutralization has the following properties:

(1) in the equation defined by pH=pKa+n log (u/ 1-u) (IV) wherein pHrepresents pH value in aqueous resinous solution or dispersion, pKa is aparameter which represents the acidity of the resin component, orrepresents the neutralization degree of the resin component, 8.0pKa, 0.5S n S 1.5 and 30% S a80%, and n is a parameter showing the extension ofthe resin in water,

(2) the resin has a glass transition temperature Tg of 60 C. or below,and

(3) the resin has an average molecular weight of 2. A coatingcomposition according to claim 1, wherein the characteristics of theresin after neutralization are such that the resin satisfies, in theEquation IV, the conditions of 8.5pKa9.5, 0.8n1.3, and 30%a80%, has aglass transition temperature Tg of 30 C. or below, and has an averagemolecular weight of 5,000 to 15,000.

3. A coating composition according to claim 2, which contains a pigmentsatisfying a relationship represented by the equation:

wherein pKa is as defined above, and pKp represents the acidity of thepigment.

4. A coating composition according to claim 3 which comprises 60 partsby weight or less of N-alkoxymethylmelamine and/ or epoxy resins and 100parts by weight of the resin components comprising 93.5-35 mole percentof the component (A), 1.5-15 mole percent of the component (B), and 5-50mole percent of the component (C).

5. A coating composition according to claim 3, where in the coatingcomposition is so prepared as to form an aqueous electrodepositioncoating bath containing 2-20% by weight of the water-soluble orwater-dispersible resin as a main component and having a specificelectroconductivity at 25 C. of 150-800 ar/cm at the time when thesolids content of the bath is 11% by weight.

6. A coating composition according to claim 5, where in thewater-soluble or water-dispersi'ble resin has been prepared by use of awater-miscible organic solvent as a polymerization medium.

7. A coating composition according to claim 6, where in thewater-soluble or water-dispersible resin employed contains -30 molepercent of the component (C).

8. A coating composition according to claim 7, wherein the component (C)comprising the compound represented by the general Formula III isN-butoxymethyl acrylamide or N-butoxymethyl methacrylamide.

9. -A coating composition according to claim 3, which comprises an epoxyresin and/or an N-alkoxymethylated melamine resin containing an alkylgroup having 1-4 carbon atoms, and a resin component comprising, as thecomponent (A), a monomer mixture formed by mixing in a molar ratio of99.9/0.140/60 at least one compound represented by the general Formula Iwith said other monomer; as the component -(B), itaconic acid ora-methyleneglutaric acid; and as the component (C), N- butoxymethylacrylamide or N-butoxymethylmethacrylamide.

10. A coating composition according to claim 9 wherein the water-solubleor water-dispersible resin has been prepared by use of the monomermixture containing an N-alkoxyalkyl acrylamide or methacrylamideobtained by mixing, in a molar ratio of 99.9/0.120/80, a compoundrepresented by the general formula:

wherein R is a hydrogen atom or a methyl group, and R is a hydrogen atomor an alkyl group having 1 to 12 carbon atoms, with itaconic acid ortat-methylene glutaric acid or an anhydride thereof and subjecting themixture to dehydration condensation with alcohol and aldehyde in thepresence of (1) an organic solvent azeotropic with water, (2)acrylonitrile, or (3) a mixture of (1) and (2).

11. A coating composition according to claim 9 wherein the water-solubleor water-dispersible resin has been prepared by use of the monomermixture containing an N-alkoxyalkyl acrylamide or methacrylamideobtained by mixing, in a molar ratio of 99.9/0.120/ 80, a compoundrepresented by the formula:

wherein R is a hydrogen atom or a methyl group, and R is a branched orstraight chain alkylene group having 1 to 3 carbon atoms, with itaconicacid or a-methylene glutaric acid or an anhydride thereof, andsubjecting the mixture to dehydration condensation with alcohol in thepresence of (1) an organic solvent azeotropic with water, or (2)acrylonitrile, or (3) a mixture of (1) and (2).

12. A coating composition according to claim 11, wherein said aqueousbath containing the water-soluble or water-dispersible resin alsoincludes, as a film formationcontrolling agent, an amphotericelectrolyte having an isoelectric point of 5.5-8.5.

13. A coating composition according to claim 12, wherein the amphotericelectrolyte is an amino acid.

References Cited UNITED STATES PATENTS 3,037,963 6/1962 Christenson26072 3,079,434 2/ 1963 Christensen et al. 26072 3,163,623 12/1964Sekmakas et al. -a 26072 FOREIGN PATENTS 1,027,813 4/1966 Great Britain26029.4

1,030,425 5/1966 Great Britain 260296 DONALD J. ARNOLD, Primary ExaminerH. MINTZ, Assistant Examiner US. Cl. X.R.

117-l32 B, 161 UT, 201; 260-29.6 NR, 29.6 TA, 29.6 HN, 78.5 R

